FIG. 1A is a perspective view of a grain grinder 101 made according to the prior art. FIG. 1B is a side sectional view of the grain grinder 101 of FIG. 1A. Referring to FIGS. 1A and 1B, the grain grinder 101 includes a body 102 that defines a cylindrical conveying volume 104 positioned to convey grain 105 from an input hopper 108 to a pair of grinding plates 112, 120. A shaft 111 is supported by bearings 128 and is positioned axially to the conveying volume 104. The shaft 111 supports a spring auger 106 that turns with the shaft to urge grain from the hopper end of the conveying volume to the pair of grinding plates 112, 120 at the output end of the cylindrical conveying volume 104. A stationary grinding plate 112 is coupled to the body 102 and positioned circumferentially to the shaft 110 such that grain may pass through an inner diameter 114 of the stationary grinding plate 112. The grain is conveyed by the spring auger 106 to a receiving volume (not shown) formed between depressions in grinding surfaces of the stationary grinding plate 112 and a rotatable grinding plate 120. A hand crank 122 may be positioned to receive human power to rotate the shaft 111, the spring auger 106, the grain meter 110, and the rotatable grinding plate 120 relative to the body 102, cylindrical conveying volume 104, and stationary grinding plate 112. The spring auger 106 urges grain from the hopper 108 to a nip between the grinding plates 112, 120. The receiving volume (not shown) may be comprised of facing hollowed sections of the grinding surfaces and configured to receive grain for initial grinding and movement to contacting regions of the grinding surfaces of the grinding plates 112, 120 located around the periphery of the grinding plates 112, 120. Grinding action between the stationary grinding plate 112 and the rotatable grinding plate 120 mills the grain into flour. The stationary grinding plate 112 and the rotatable grinding plate 120 may be about 5 inches in diameter.
Optionally, a person may provide a power source to the shaft 111. For example, the hand crank 122 may be operatively coupled the shaft 111. A person may provide rotational motion to the shaft 111, the spring auger 106, and the rotatable grinding plate 120. Alternatively, a person or a motor constrained to providing no more rotational power that the person may provide rotational motion to a pulley 126 that may include a V-groove capable of receiving rotational energy from a V-belt (not shown). The V-belt may be coupled to another human-powered source such as a stationary bicycle, or may be coupled to a motor.
While the grain grinder 101 is capable of producing flour, it is not capable of effectively grinding materials other than dry grains, nor is it capable of effectively producing a paste or butter. What is needed is a mechanism capable of milling oily or moist materials such as nuts into nut butters such as peanut butter.